Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 32: Heterogeneous Catalysis I

O 32.7: Talk

Tuesday, March 18, 2025, 12:00–12:15, H25

U-Ce charge transfer in epitaxial Ce_1−xU_xO₂ films grown on Ru(0001): consequences for thermochemical water splitting — •Carlos Morales¹, Rudi Tschammer¹, Thomas Gouder², Hicham Idriss³, and Jan Ingo Flege¹ — ¹Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology, Cottbus, Germany — ²European Commission, Joint Research Centre (JRC), Karlsruhe, Germany — ³Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Reducible metal oxides are crucial in applications like catalysis and solar energy conversion. Among these, cerium oxide (CeO₂) stands out for its stability and activity, yet its reduction requires high energy. Ceria doping or mixing with other elements has been proven successful in increasing the conversion from Ce⁴⁺ to Ce³⁺. Uranium cations are the most suitable candidates: substituting a fraction of Ce⁴⁺ by U⁴⁺ results in a charge transfer that promotes the formation of Ce³⁺ and U⁵⁺ states. The fundamental study of the charge transfer process requires model systems, as heat and mass transfer limitations are largely absent compared to polycrystalline powders. By in-situ X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED), we explored the redox properties and structural stability of epitaxial (111)-oriented Ce_1−xU_xO₂ on Ru(0001). The as-grown films, prepared by reactive direct current sputtering from metallic targets, show a high Ce⁴⁺ to Ce³⁺ conversion, reversible upon reducing-oxidizing cycles. The experimental results are discussed in the light of density function theory (DFT) calculations.

Keywords: CeO2; Uranium; Epitaxy; XPS; DFT